UMA metrics for use count of wheel and touch scrolls.

cc/trees/layer_tree_host_impl.h

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_TREES_LAYER_TREE_HOST_IMPL_H_
 #define CC_TREES_LAYER_TREE_HOST_IMPL_H_
 
 #include <stddef.h>
 
 #include <bitset>
@@ skipping 692 matching lines @@
   void UpdateRootLayerStateForSynchronousInputHandler();
 
   bool ScrollAnimationUpdateTarget(ScrollNode* scroll_node,
                                    const gfx::Vector2dF& scroll_delta,
                                    base::TimeDelta delayed_by);
 
   void SetContextVisibility(bool is_visible);
   void ImageDecodeFinished(const base::Callback<void(bool)>& embedder_callback,
                            bool decode_succeeded);
 
+  void UpdateScrollSourceInfo(bool is_wheel_scroll);
+
   using UIResourceMap = std::unordered_map<UIResourceId, UIResourceData>;
   UIResourceMap ui_resource_map_;
 
   // Resources that were evicted by EvictAllUIResources. Resources are removed
   // from this when they are touched by a create or destroy from the UI resource
   // request queue.
   std::set<UIResourceId> evicted_ui_resources_;
 
   CompositorFrameSink* compositor_frame_sink_;
 
@@ skipping 124 matching lines @@
 
   std::unique_ptr<LayerTreeMutator> mutator_;
 
   std::unique_ptr<PendingTreeDurationHistogramTimer>
       pending_tree_duration_timer_;
 
   // These callbacks are stored here to be transfered to the main thread when we
   // begin main frame. These callbacks must only be called on the main thread.
   std::vector<base::Closure> completed_image_decode_callbacks_;
 
+  // These are used to transfer usage of touch and wheel scrolls to the main
+  // thread.
+  bool has_scrolled_by_wheel_;

[danakj, 2017/03/16 15:19:21]

where do these get init to false?

[sahel, 2017/03/17 21:02:34]

Done.

+  bool has_scrolled_by_touch_;
+
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_